The present invention relates to the general fields of pharmaceuticals and cancer chemotherapy, particularly to the areas of cytotoxic antitumor agents and DNA intercalating agents. The invention also relates to medicinal chemistry, and the fields of acridone and 1,8-naphthalimide organic chemistry.
A number of acridine-based compounds which exhibit antitumor activity have been reported. Cholody et al. described 5-[(amino-alkyl)amino]-imidazo[4,5,1-de]acridin-6-ones as a novel class of antineoplastic agents (Cholody et al., J. Med. Chem. 33:49-52 (1990)); 8-substituted 5-[(aminoalkyl)amino]-6H-v-triazolo[4,5,1-de]acridin-6-ones as potential antineoplastic agents (Cholody et al., J. Med. Chem. 33:2852-2856 (1990)); and chromophore-modified imidazoacridones and their activity against murine leukemias (Cholody et al., J. Med. Chem. 35:378-382 (1992)). Capps et al. described 2-(aminoalkyl)-5-nitropyrazolo[3,4,5-kl]acridines as a new class of anticancer agents (Capps et al., J. Med. Chem. 35:4770-4778 (1992)). More recently, an 8-hydroxyimidazo[4,5,1-de]acridin-6-one, C1311, has entered clinical trials (Burger et al., Br. J. Cancer 74:1369-1374 (1996); Idem, Br. J. Cancer 81:367-375 (1999)).
It is believed that DNA is the primary target for these compounds, and that they bind to DNA by intercalation. There is good evidence that intercalation of DNA by these drugs disrupts the activity of eukaryotic topoisomerase II (Capranico and Zunino, Eur. J. Cancer 28A:2055-2060 (1992); Beck et al., Cancer Chemother. Pharmacol. 34(Supp):S14-S18 (1994); Nitiss and Beck, Eur. J. Cancer 32A:958-966 (1996)).
Braxc3x1a et al. have described naphthalimides with basic side chains which have anti-tumor activity (Braxc3x1a et al., Cancer Chemother. Pharmacol., 4:61-66 (1980); Eur. J. Med. Chem., 16:207-212 (1981); U.S. Pat. No. 4,204,063; U.S. Pat. No. 5,183,821). Examples which have reached the clinic include the compounds amonafide (Kornek et al., Eur. J. Cancer, 30A:398-400 (1994)) and mitonafide (Rosell et al., Invest. New Drugs, 10:171-175 (1992); Llombart et al., ibid., 177-181). Numerous other naphthalimide derivatives, among them nafidimide and azonafide, have been studied as well (Sami et al., J. Med. Chem. 39:4978-4987 (1996) and references therein).
The strong binding to nucleic acids of bis-intercalators, which contain two planar aromatic systems joined by suitable linker, has long been known (Canellakis et al., Biochim. Biophys. Acta 418:277-283 (1976)). Based upon the anti-tumor activity of the mono-intercalators, which were presumed to function by DNA intercalation, bis-intercalating compounds have been intensely studied as potential antitumor agents. It has been generally assumed that these compounds function by bis-intercalation of both chromophores into DNA.
Chen et al. studied diacridines as potential bifunctional intercalators (Chen et al, J. Med. Chem. 21:868-874 (1978)). Gaugain et al. described the synthesis and conformational properties of an ethidium homodimer and an acridine ethidium heterodimer (Gaugain et al., Biochemistry 17:5071-5078 (1978)). Sinha et al. described the synthesis and antitumor properties of bis(quinaldine) derivatives (Sinha et al., J. Med. Chem. 20:1528-1531(1977)). Roques et al. described the antileukemic activity of pyridocarbazole dimers (Roques et al., Biochem. Pharmacol. 28:1811-1815 (1979)). Wright et al. and Le Pecq et al. described bis-intercalating diacridines and the relationship of structure to DNA Binding (Wright et al., Biochemistry, 19:5825-5836 (1990); Le Pecq et al., Eur. J. Biochem., 180:359-366 (1989). Pelaprat et al. described 7H-pyridocarbazole dimers as potential antitumor agents (Pelaprat et al., J. Med. Chem. 23:1336-1343 (1980)). Cholody et al., disclosed bis(imidazoacridone) derivatives active against colon tumor cells (Cholody et al., J. Med. Chem. 38:3043-3052 (1995) and studied the mechanism of action (Hernandez et al., Cancer Res. 55:2338-2345 (1995); see also Michejda et al., U.S. Pat. No. 5,508,289 and international application WO 97/38999, the entire disclosures of which are incorporated herein by reference. The same group of workers also disclosed certain bis(triazoloacridone) compounds active against HIV transcription (Turpin et al., Antimicrob. Agents Chemother. 42:487-494 (1998).
Braxc3x1a et al. have described bis-naphthalimides as a class of antitumor agents (Braxc3x1a et al., Anti-Cancer Drug Design 8:257-268 (1993)). Kirshenbaum et al. described DMP-840, a bis-naphthalimide with promising antitumor activity (Kirshenbaum et al. Cancer Res. 54:2199-2206 (1994); and Nitiss et al. discussed the mechanism of action of DMP-840 (Nitiss et al., Biochemistry 37:3078-3085 (1998)).
Braxc3x1a et al., in U.S. Pat. Nos. 4,874,863; 5,616,589; and 5,789,418 (all of which are incorporated herein by reference in their entirety), describe numerous bis(1,8-naphthalimide) compounds which have anti-tumor activity. Ardecky described similar acenaphthalene-derived bis-imide intercalators (Ardecky et al, U.S. Pat. No. 5,086,059), as did Cherney and Seitz in U.S. Pat. No. 5,359,070 (both of which are incorporated by reference herein). Cherney et al. have also described benzo- and hetero-fused bis(1,8-naphthalimide) derivatives which have anti-tumor activity (Cherney et al., Bioorg. Med. Chem. Letters, 7:163-168 (1997); U.S. Pat. No. 5,585,382, incorporated by reference herein). Braxc3x1a et al. have also disclosed benzo-fused 1,8-naphthalimides derived from anthracene1,9-dicarboxylic acid (Braxc3x1a et al., J. Med. Chem., 40:449-454 91997)). Sun et al. have described an extensive series of bis-naphthalimide antitumor agents (Sun et al., WO 92/17453; U.S. Pat. No. 5,206,249; U.S. Pat. No. 5,206,250; U.S. Pat. No. 5,376,664; U.S. Pat. No. 5,488,110; and U.S. Pat. No. 5,641,782, all of which are incorporated herein by reference in their entirety). Weis et al. described bis (1,8-naphthalimide anti-tumor agents having variations in the linker moiety (Weis et al., U.S. Pat. No. 5,604,095, incorporated herein by reference).
Many factors, such as physico-chemical characteristics of the planar chromophores, nature of the linking chain (length, rigidity, and ionization state), position of attachment, and other factors, strongly influence the binding with DNA and the biological action of these compounds. However, it has been found that although such compounds exhibit high affinity for DNA, there is little correlation between DNA binding affinity and cytotoxicity or antitumor activity. For example, some bis-intercalators are cytotoxic, while closely related compounds are merely cytostatic.
Since structure-activity relationships in the class of bis-intercalators in relation to their in vivo antitumor action remain unclear, it has not been possible to predict which structures will show such activity, even given their binding affinity for DNA. Small structural modifications can substantially alter the pharmacological properties of a DNA intercalator without similarly affecting DNA binding. Accordingly, research is still ongoing to find DNA intercalating compounds with high antineoplastic activity, especially those having selective activity towards specific tumors.
Compounds designed as potential bis-intercalating agents have typically consisted of two identical planar aromatic ring systems (xe2x80x9cchromophoresxe2x80x9d) which are capable of intercalation between the base pairs of double-stranded DNA, joined by a flexible linker of suitable length. Compounds having two identical chromophores are referred to herein as xe2x80x9csymmetricalxe2x80x9d. Previous workers in the field have generally assumed that the mechanism of action of bifunctional intercalators depends upon intercalation of both chromophores into DNA (hence the generic term xe2x80x9cbis-intercalatorxe2x80x9d). Bis-intercalated DNA complexes have in fact been observed experimentally (Peek et al., Biochemistry 33:3794-3800 (1994); Shui et al. Curr. Med. Chem. 7:59-71 (2000)).
Accordingly, the design of these agents has most often been based on previous findings concerning structural requirements for bis-intercalation of symmetrical compounds. Most workers have assumed that if a given chromophore is discovered to be a very tight-binding DNA intercalator, then the linking of two such chromophores will generate a superior bifunctional intercalator. Given two identical, linked, tight-binding chromophores, previous workers proceeded to optimize the distance and geometry between the two by modifying the linker, and sought to obtain additional binding interactions between the linker and the DNA.
Thus, once a promising chromophore has been identified, symmetrical bis-intercalators are usually prepared, and attention is focused thereafter on chromophore substituents and on modifications to the linker moiety in attempts to improve anti-tumor activity. There have been a few studies directed at bis(1,8-naphthalimides) which are rendered asymmetric by virtue of differing chromophore substitution, with improvements in solubility and occasional improvements in biological activity being noted (Cherney et al., U.S. Pat. No. 5,359,070, incorporated herein by reference; Idem., Bioorg. Med. Chem. Lett. 7:163-168 (1997); Patten et al., U.S. Pat. No. 5,585,382, incorporated herein by reference). Prior to the present invention, however, there has been very little work directed to substantially unsymmetrical bifunctional intercalators.
This invention relates to a novel class of unsymmetrical imidazoacridone-naphthalimide based DNA bifunctional intercalators, and their use as antineoplastic agents. The compounds are 6H-imidazo[4,5,1-de]acridin-6-ones attached through an amino-containing linker at the 5-position to the 2-position of a 1,8-naphthalimide. These compounds, having two different chromophores, have been found to be exceptionally potent anti-tumor agents, superior to symmetrical bifunctional intercalators containing either chromophore alone.
The invention is most broadly directed to (a) compounds of structure 1, (b) methods of their preparation, and (c) methods of treating diseases characterized by excess cellular proliferation, such as cancer, with these compounds. The compounds of the invention have general structure: 
wherein
A=an alkyl linker, such as for example (CH2)m or (CHR)m;
B=an amino-containing linker, such as for example NRxe2x80x2, NRxe2x80x2(CH2)nNRxe2x80x3, hexahydropyrimiidine-1,3-diyl, piperazine-1,4-diyl, 4-aminopiperidine-1,4N-diyl, or 1,4-diazacycloheptane-1,4-diyl;
D=an alkyl linker, for example (CH2)p or (CHR)p;
Y=any common aromatic substituent, such as for example R, COR, CO2R, CONRRxe2x80x2, SR, SOR, SO2R, SO2CF3, SO2NRRxe2x80x2, OR, OCF3, OCOR, OCONRRxe2x80x2, NO2, NRRxe2x80x2, CN, Ph, CF3, NRCORxe2x80x2, NRCONRxe2x80x2Rxe2x80x3, NRC(NRxe2x80x2)NRxe2x80x3Rxe2x80x2xe2x80x3, NRCOCF3, NRSO2Rxe2x80x2, NRSO2CF3, or halogen;
R=H, CF3, lower alkyl, amino-lower alkyl, or hydroxy-lower alkyl;
Rxe2x80x2, Rxe2x80x3=R, C(O)R, or SO2R; and
m, n, and p=2-6.